Walter Cai <wzcai92@gmail.com> writes:
> I (a graduate student) am currently trying to modify a postgres instance
> slightly to incorporate my modified cardinality estimates. In order to run
> these experiments I'm hoping to access the raw values for selections
> predicates from within the calc_joinrel_size_estimate method (in costsize.c).
> For example, if the restriction
> WHERE name_attr = "example_str"
> appears in the query, I'd like to get the "name_attr" and "example_str"
> values. If possible, I would very much appreciate the help.
It's pretty unclear what you mean by "raw values". What you're actually
going to be dealing with in that part of the code is a List of
RestrictInfo nodes, one for each relevant WHERE clause. The one
representing this particular clause would contain an OpExpr node
representing the "=" operator, and the two inputs of the operator
would be a Var node representing the name_attr column and a Const
representing the 'example_str' literal. You could pull the value
of the literal out of the Const node easily enough, but I don't
understand what you're looking for with respect to the Var.
regards, tom lane